1. Field of the Invention
The present invention generally relates to electronic circuits and, more specifically, to the protection of data contained in an electronic circuit against fraud attempts aiming at reading said data. The data may be digital quantities supposed to remain secret (that is, within the electronic circuit), for example, access codes or passwords, or specific steps of algorithms and, more generally, any digital data this is not supposed to be communicated in an uncontrolled fashion.
The present invention will be described hereafter in relation with an example of application to smart cards, but it more generally applies to any electronic circuit containing data with a controlled circulation, be the circuit on a smart card, isolated, or assembled on an electronic board of a more complex device.
2. Discussion of the Related Art
When an electronic circuit is to manipulate data which are not intended to be communicated in an uncontrolled fashion, it is equipped with software and/or hardware mechanisms of detection and protection against different attack attempts aiming at hacking these data. Among such attacks, some disturb the electronic circuit operation (for example, attacks known as differential fault analysis attacks—DFA) or cut off the electronic circuit power supply.
A problem of conventional protection mechanisms, be they software or hardware, is that it is difficult to make out a fraud attempt from an incidental disturbance. Now, the action to be taken after a malfunction may be different according to whether it is an attack or an incidental malfunction. In the first case, the electronic circuit operation should generally be blocked to avoid the outputting of data supposed to remain confidential. In the second case, it may be desirable to allow a restarting of the circuit.